The nuclear power generation and other industries require radiation hardened camera systems for monitoring areas exposed to radiation. Typically, such camera systems consist of a radiation-hardened remote head positioned within the irradiated area, and a camera control unit (CCU) located at the control room or other area accessible to human operators. The remote head and CCU may communicate via a cable.
Basic Charge Injection Device (CID) imaging technology is described by Michon and Burke in “CID image sensing,” Charge-Coupled Devices, (Springer, 1980), which is incorporated herein by reference. Thermo Fisher Scientific CIDTEC's MegaRAD™ camera, a solid state radiation-hardened monochrome camera based on CID technology has been available for a decade. Moreover, the use of OD-based color image sensors at the remote head is known, as well. However, while the CID benefits from inherent robustness in high-radiation environments, as with any solid state device, silicon-based or otherwise, under radiation, the CID image sensors are susceptible to damage by both ionizing energy loss (IEL) and non-ionizing energy loss (NIEL).
As used herein, and in any appended claims, the term “high-radiation environment” will refer to environments in which equipment is exposed to radiation of up to 106 rad/hr. “Ionizing radiation” shall refer to radiation of sufficient energy to give rise to ionization of the gate oxide of an imager, whereas “non-ionizing radiation,” as used herein and in any appended claims, shall refer to radiation capable of displacing silicon atoms in the imager substrate, unless the context dictates otherwise. Thus, insofar as IEL ionizes the gate oxide, IEL may result in degraded performance of the MOSFET (Metal-Oxide Semiconductor Field Effect Transistor) devices used for amplification of the photo-induced charge. The MOSFET degradation is mainly observed as a shift in the threshold voltage (Vth) of the device. This makes it difficult to turn an n-type MOSFET (NFET) ‘off’ or turn a p-type MOSFET (PFET) ‘on’.
NIEL can lead to bulk damage such as displacement of silicon atoms in the epitaxial (EPI) layer. Such displacement gives rise to permanent defects which are, in turn, the primary cause of elevated dark current and poor charge transfer efficiency (CTE).
Against this background, there is a need in the art for a radiation-hardened CID-based camera system that avoids performance degradation arising from the IEL and NIEL effects described above and that provides for operator placement at significant distances.